Cardiac output is determined by.

Which of the following cells phagocytose microorganisms rapidly?

$A$: $A$ portal system consists of veins that start from capillaries and end into capillaries.
$R$: All vertebrates have a hepatic portal system.

Select the correct option regarding the clotting of body fluids in a test tube.

Assertion $A$: Anemia is sometimes observed in humans.
Reason $R$: There is a deficiency of iron and copper in the human body.
Which option is correct for Assertion $A$ and Reason $R$?

The given figure shows a schematic plan of blood circulation in humans with labels $A$ to $D$. Identify the label and give its functions.